The present invention relates to a cutting blade suitable for cutting a semiconductor plate, particularly a semiconductor plate obtained by resin-molding a plurality of semiconductor chips which are arranged in a matrix form and of which adjacent semiconductor chips are connected with each another via a plurality of electrodes, along cutting lines formed at the intermediate portions of the above electrodes.
In the production process of a semiconductor device, semiconductor chips are individually produced by forming a circuit such as IC or LSI in a plurality of areas arranged in a lattice form on the surface of a substantially disk-like semiconductor wafer and dicing the areas having circuit formed therein along predetermined cutting lines called xe2x80x9cstreetsxe2x80x9d. The thus divided semiconductor chips are packaged, and the semiconductor chip package is widely used in electric appliances such as portable telephones and personal computers.
Lighter and smaller electric appliances such as portable telephones and personal computers are now in growing demand, and packaging technologies called xe2x80x9cchip size package (CSP)xe2x80x9d which can reduce the size of a semiconductor chip package have been developed. As one of the chip size package (CPS) technologies, a packaging technology called xe2x80x9cQuad Flat Non-lead Package (QFN)xe2x80x9d has been put into practice. This packaging technology called xe2x80x9cQFNxe2x80x9d will be described with reference to FIG. 6 and FIG. 7.
According to the packaging technology called xe2x80x9cQFNxe2x80x9d, a semiconductor plate 10 is formed by molding a plurality of semiconductor chips 101 (see FIG. 7) arranged in a matrix form and a plurality of electrodes 102 for connecting adjacent semiconductor chips as shown in FIG. 6, together with a resin 103. This semiconductor plate 10 is cut along cutting lines 104 called xe2x80x9cstreetsxe2x80x9d formed at the intermediate portions of the electrodes 102 which connect adjacent semiconductor chips so that it is divided into individually packaged semiconductor chips 100 (semiconductor packages) as shown in FIG. 7. The above electrodes 102 and the above cutting lines 104 are formed of a metal plate such as a copper plate.
The above semiconductor plate 10 is generally cut by a precision cutting machine called xe2x80x9cdicing machinexe2x80x9d. This dicing machine has a cutting blade having annular abrasive grain layer, and the cutting blade and the semiconductor plate relatively move along the cutting lines 104 formed in the semiconductor plate 10 to cut the semiconductor plate 10 along the cutting lines 104 and divide it into individual semiconductor packages 100 as shown in FIG. 7.
However, the electrodes 102 which connect adjacent semiconductor chips 101 in the state of the above semiconductor plate 10 are formed of a metal plate such as a copper plate, and when the intermediate portion of the electrode 102 is cut with the cutting blade 20 along the street 104, as shown in FIG. 8, such a problem exists that burrs 110 are generated and cause a short-circuit between the electrodes 102 of each semiconductor package 100 as shown in FIG. 7. It has been found that burrs are generated when the electrodes 102 made of a soft and viscous material such as copper are cut and forced out on both sides of the cutting blade 20 because the contour surface of the cutting blade 20 has substantially a convex arc surface in cross section.
The Applicant proposes in Unexamined Japanese Patent Application No. 2000-307541 a cutting blade composed of an annular central abrasive grain layer and outer abrasive grain layers formed on both sides of the central abrasive grain layer, the central abrasive grain layer having a smaller diameter than the outer abrasive grain layers to form an annular depression in the peripheral surface, as a cutting blade which can prevent the generation of burrs when the above semiconductor plate is cut with the cutting blade along the cutting lines.
Although the semiconductor plate can be cut with the above cutting blade without generating burrs, the cutting blade is not satisfactory from the standpoint of production, and further improvement of the cutting blade is desired.
It is an object of the present invention to provide a cutting blade which can prevent the generation of burrs when the above semiconductor plate is cut along the cutting lines, and can be easily produced.
According to the present invention, the above object can be attained by a cutting blade having an annular cutting edge portion composed of electroformed abrasive grain layers in which abrasive grains are fixed by electroforming, wherein the annular cutting edge portion is composed of a central electroformed abrasive grain layer and outer electroformed abrasive grain layers formed on both sides of the central electroformed abrasive grain layer; and the central electroformed abrasive grain layer is an abrasive grain layer having a low concentration, and the outer abrasive grain layers are each an abrasive grain layer having a higher concentration than the central electroformed abrasive grain layer.
It is desired that the above central electroformed abrasive grain layer be formed of an abrasive grain layer having a concentration of 0 to 100 and that the outer electroformed abrasive grain layers be formed of each an abrasive grain layer having a concentration of 200 to 300.
The grain diameter of the above abrasive grains is set to {fraction (1/10)} to ⅓ the thickness of the above annular cutting edge portion. It is desired that the thickness of the annular cutting edge portion be set to 200 to 300 xcexcm and that the grain diameter of the abrasive grains be set to 20 to 60 xcexcm. Further, the abrasive grains are desirably diamond abrasive grains.